Harold Froehlich, who died Saturday at 84, designed and built the Alvin, the small submersible that recovered a lost hydrogen bomb, sifted through the wreckage of the Titanic, and discovered giant red tube worms living at deep water thermal vents near the Galapagos.

Froehlich, an engineer who served aboard oil tankers in the Pacific during World War II, conceived and built the Alvin while working in the Minneapolis engineering division of General Mills. While the company is today known mainly for brands such as Betty Crocker and Wheaties, it was in the wake of World War II also an important defense contractor. The same engineers who designed extrusion machinery for Cheerios worked in the war effort. The company helped develop the black box recording technology for airplanes.

In the 1950s, Froehlich patented designs on high-altitude reconnaissance balloons to spy on the U.S.S.R., and worked on an arm for the Navy bathyscaphe Trieste. When he heard that the Office of Naval Research was looking for a design for a small, maneuverable research vessel to perform at great depth, he designed an early version of the Alvin that he dubbed the Seapup, according to “50 Years of Ocean Discovery,” a history published by the National Academies Press. Woods Hole Oceanographic Institute has operated the Alvin since it was commissioned, in 1964.

Froehlich’s proposal beat out others proposed by the Reynolds Metals Co. and North American Aviation; a cereal company more than 1,000 miles away from the nearest ocean ended up building a breakthrough submersible. “The Bureau of Ships was skeptical about a Wheaties company designing a submarine,” Froehlich told Minnesota Public Radio in 2003. “They really didn’t want to see this precedent set.”

With a crew numbering about 35, Froehlich built the Alvin, which was named for a Woods Hole engineer who had shepherded its funding, Allyn Vine. (There is also persistent speculation that it was named for the high-voiced animated chipmunk.)

As designed, the Alvin could descend to 2,000 meters and zip along the sea floor at a breakneck one to two miles an hour with a crew of a pilot and two scientists. Its small size made it easy to lift out of the water to perform maintenance, unlike more cumbersome bathyscaphes, which had to be much larger to ensure neutral buoyancy with sophisticated technology. The Alvin just carried 1,000 pounds of ballast to descend, dropped half of it to sit on the ocean floor, and jettisoned the rest to rise. It was an idea Froehlich imported from his balloon work, he told the Minneapolis Star-Tribune in 1993. “The same basic engineering principle is used to control both — ballast.”

Froehlich participated in the first few shallow proof-of-concept dives, then retired to work on other projects.

The Alvin, which he said he regarded as his “third child” — he also had a son and a daughter — went on to a pioneering career in science and international politics. It was responsible for discovering new sea floor species from an early voyage off Martha’s Vineyard, but the submersible first made headlines in 1966, when it recovered a hydrogen bomb that had fallen from an American bomber on patrol near the coast of Spain.

Later, during the mid-1970s, the Alvin discovered 12-foot red tube worms and other forms of life that derived energy from sulfur-rich waters near volcanically active sea floor vents. In 1986, it produced stunning footage of the Titanic that helped establish that popped rivets helped to speed the liner’s sinking. A robotic arm extended from the Alvin failed to turn the tumbler on the ship’s safe. Over the years, the Alvin was greatly enhanced during periodic overhauls that replaced its stainless steel frame with titanium, enlarged its windows, and eventually replaced every single part of it, although the same basic shape persists.

Froehlich’s involvement with the Alvin stopped after it was christened. He worked for Programmed and Remote Systems Corp., a General Mills spinoff that produced robotic submarine arms. He later worked on buoyboard generators and, at 3M Corp., became a pioneer in the development of surgical staple technology.

“My only regret,” he told the Star-Tribune, “is that Alvin had to leave Minnesota.”